Current systems used to refill vehicle storage tanks with high pressure hydrogen or compressed natural gas require an expensive flow meter in a high pressure environment. Because of the expense and complexity of high pressure gas metering, the use of flow meters at retail fuel depots is not likely to be implemented. A refilling system not utilizing a flow meter is less expensive; however, currently known non-flow meter systems are operationally deficient. Pressure differences, for example, when pressure is at 3600 psi for compressed natural gas (CNG) and 5000 psi and 10,000 psi for hydrogen (corresponding to flow volume and gas quantity refilled at a refueling depot pump), are too small for meter systems to analyze and the flow monitoring system has a very low tolerance of flow disturbances.
Metering systems have been proposed, such as described in JP 2004084808 wherein Tomotaka shows a hydrogen gas supply system for a vehicle with a plurality of high-pressure hydrogen tanks. Each of the tanks is provided with a filling valve, a discharge valve, a pressure sensor and a temperature sensor. A vehicle control unit controls the filling valve and the discharge valve on the basis of parameters measured by a temperature sensor and a pressure sensor. U.S. Pat. No. 5,884,675, Krasnov, shows a cascade system for fueling compressed natural gas with two banks of cylinders. The refueling system empties the tanks in banks, one at a time, by refueling CNG vehicles using a plurality of refueling tanks. A pressure-limiting valve limits pressure in the vessel tanks to 3000 psi. When one bank is exhausted of CNG, the pump pistons stop moving, the pressure at the outlets drops to below 3000 psi, and the pressure at the inlets increases. This difference in pressure is sensed, causing the control panel to change banks. DE 19729267 (corresponding U.S. Pat. No. 6,095,207, Enders) shows a seal for a petrol refill opening in vehicle in which the internal pressure of the container above the liquid level is sensed by a sensor connected to the control unit. A differential pressure created by gas leakage from the container is sensed and refueling status is detected.
Other metering systems are described in US publication 20040069414, Chuang et al.; U.S. Pat. No. 6,044,873 to Miller; U.S. Pat. No. 5,029,622 to Mutter; U.S. Pat. No. 3,999,936 to Hasselmann et al.; JP 09096400 to Yuji et al.; EP 1205704 to Mutter; WO 9836211 to Kopl et al.; WO 9736130 (in Russian); and DE 4212626 to Seifers.
Thus, while certain pressure differential systems for measuring fuel input at refill depots are known in gas refueling operations (most simply, check valves), and the art teaches that refueling is complete when the pressure difference monitored in sensors at the station and at the vehicle tank, dP=P1station−P2vehicle, is zero or approaches slightly greater than zero, there remains a need for an inexpensive, relatively simple system for controlling the special situations involving a high pressure fuel gas volume or quantity refilled into a vehicle. Accurate control is a requirement before a high pressure gas retail depot infrastructure can be developed and implemented for widespread commercial use in consumer vehicle and commercial vehicle applications.